Jim Dollard has an extensive background in codes and standards. If you have a query about the National Electrical Code (NEC) , Jim will help you solve it. Send questions to email@example.com. Answers are based on the 2017 NEC .
Selective coordination for elevators
When applying the rules for selective coordination for disconnects that supply elevators, I am not sure what to coordinate. Starting with the fused disconnect supplying each machine and going upstream, do all of the upstream overcurrent protective devices (OCPDs) need to be selectively coordinated with every other device?
No, the requirement for selective coordination is in 620.62. This applies to installations where more than one driving machine disconnecting means is supplied by a single feeder. Where that occurs, the OCPDs in each disconnecting means must selectively coordinate with any other supply-side OCPD.
Looking at just one of the fused disconnects supplying the driving machine, let’s assume there are three upstream OCPDs. Each of those devices must selectively coordinate with the overcurrent protection in the disconnecting means supplying the machine. The three upstream devices (A, B and C) are not required to selectively coordinate with each other. If we name the fused disconnect that supplies the machine as D, the selective coordination would be as follows: D must selectively coordinate with A, B and C. However, C is not required to selectively coordinate with B or A, and B is not required to selectively coordinate with A.
Capacitor at the motor
Where a capacitor is installed at a motor, is a fused disconnect required for the capacitor? Are the conductors from the capacitor to the motor rated at motor full load current or the rating of the capacitor?
Section 430.27 requires that a capacitor installed in a motor circuit comply with 460.8 and 460.9. Section 460.8 requires that the ampacity of the conductors from the capacitor to the motor be sized at not less than 135 percent of the rated current on the capacitor. Additionally, these conductors must be sized at not less than one-third the ampacity of the motor circuit conductors. Overcurrent protection is not required where a capacitor is connected on the load side of the motor overload protection. A disconnect is not required for a capacitor connected on the load side of the motor controller.
Note that 460.9 modifies the setting of the motor overloads where a capacitor is installed on the load side of the overload device. The rating or setting of the motor overload device must be determined based upon the improved power factor of the motor circuit. This does not impact the sizing of the motor circuit conductors.
Is maintenance a requirement?
Does the NEC require maintenance of equipment? As a facilities manager, I have concerns because the owner did away with all preventive maintenance a few years back as a cost-saving measure.
The NEC is an installation code, and its purpose is the practical safeguarding of people or property from hazards that may arise from the use of electricity. The adequacy of this Code is addressed in 90.1(B), which states that compliance with all installation requirements and proper maintenance will result in an installation that is essentially free from hazard. There are many installation requirements in the Code such as, but not limited to, equipment being readily accessible with adequate working space to allow safe maintenance.
The NEC also contains multiple requirements that prescriptively mandate that only qualified people perform maintenance on different types of equipment. There are specific requirements for emergency, legally required standby and critical operations power systems in articles 700/701/708 related to maintenance. The scope of these articles clarifies that they cover the installation, operation and maintenance of these systems. Sections 700/701.3(C) and 708.6(C) require that these systems be maintained in accordance with manufacturer’s instructions and applicable industry standards. Additionally, 700/701.3(D) and 708.6(D) require a written record of all maintenance performed on these systems.
The sections referenced in this response are examples of NEC requirements that mandate equipment maintenance. It is important to understand that the scope of this Code clarifies that, without proper maintenance, the electrical installation may not be free from hazard. See NFPA 70B for information on recommended practices for electrical equipment maintenance.
EMT expansion fittings
An owner asked about the bonding around expansion fittings that we used where needed on an installation of electrical metallic tubing (EMT). We purchased the fittings from a reputable manufacturer, and it is my opinion that the bonding is inherent to that fitting. What do I tell the owner?
EMT, factory elbows and all associated fittings are required to be listed by 358.6. This means that the expansion fittings must be listed. The UL product category for these expansion fittings is FKAV. These fittings are considered suitable for bonding in accordance with the NEC as part of their listing. I suggest that you provide the owner with a picture of the product carton or one of the expansion fittings with the listing mark and manufacturer name along with the general information for UL product category FKAV, which covers EMT connectors, couplings and expansion fittings from trade sizes ½-inch through 4 inches.
In a mechanical room with no feasible way to get to the ceiling, we piggybacked a ¾-inch conduit onto an existing 1-inch conduit. Our inspector took exception to that and had us reroute the conduit along the wall where we could drill anchors. Does the NEC prohibit supporting one conduit from another? To be honest, we see that all the time. I could not find anything related in Article 358.
In general, the answer is no. However, the NEC does permit a raceway to be used as a means of support under three specific conditions. This is a general rule for all raceways and is found in 300.11(C). Raceways may be used as a means of support where the raceway or the support is identified as a “means of support.” The term “identified” is defined in Article 100, and the associated informational note explains ways to determine suitability for a specific purpose including, but not limited to, being listed. Where a raceway contains power supply conductors (e.g. heating or air conditioning equipment) and there is an associated Class 2 cable to control the equipment supplied by the conductors in the raceway, the Class 2 circuit conductors are permitted to be supported by that raceway. The last permission for using a raceway as support is for boxes or conduit bodies installed in accordance with 314.23 and for the support of luminaires in accordance with 410.36(E).
Panelboard rated for aluminum conductors
I recently read that, if we are going to terminate aluminum conductors in a panelboard, it must be listed as such. How can I make that determination? I understand that the circuit breakers will be marked for copper, aluminum or both and that is seen on the breaker. Where is the marking? We have the cans mounted, but there is no such labeling.
Panelboards are typically installed in a cabinet (as stated in your question). It is possible but not likely for the marking to be on the cabinet. The panelboard itself is installed inside the cabinet. A panelboard recognized for use with aluminum may need to be larger due to increased conductor size as compared to copper. There is typically a wiring diagram or a nameplate to indicate the permitted conductor types. There are multiple ways it may be marked to determine the types of conductors permitted. These include but are not limited to: marking “AL,” “CU,” “AL/CU,” “Use Copper Wire Only” or “Use Copper or Aluminum Wire.”
Duplex receptacles and 210.21(B)
Where a 20-ampere (A) individual branch circuit is installed and terminated into a single duplex receptacle, what is the required rating of the receptacle? We have an ongoing debate on 15A and 20A devices and how the rules in Article 210 apply here.
We dealt with a question on receptacle application in the past, but this issue is not going away. The problems here are a definition of “receptacle” (which essentially contains multiple definitions), misunderstanding types of branch circuits and the way we use the term receptacle in the field. Article 100 defines an individual branch circuit as a branch circuit that supplies only one utilization equipment. Article 100 also defines a receptacle as a contact device installed at the outlet for the connection of an attachment plug. This definition goes further and explains that a single receptacle is a single contact device with no other contact device on the same yoke and a multiple receptacle has two or more contact devices on the same yoke. The commonly used term “duplex receptacle” is a multiple receptacle in the Code , but in the field, we consider it a single receptacle.
Your question is about a branch that terminates into a single duplex receptacle (multiple receptacle per the definition). More than one utilization equipment can be supplied because there are two contact devices. Therefore, we do not have an individual branch circuit, and the requirements of 210.21(B)(3) apply. Since there is more than one receptacle (per the definition of receptacle), it is permitted to use 15A or 20A devices on the 20A branch circuit.